This application claims the priority of German application 198 37 180.2,filed in Germany on Aug. 17, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for condensing a drafted fiber strand in a condensing zone between the front roller pair of a drafting unit and a delivery roller pair, which apparatus includes an air permeable and suctioned sliding surface, which is movable and in contact with the fiber strand, under which sliding surface a suction slit, stationarily arranged and extending essentially in transport direction of the fiber strand, is located.
An apparatus of this type is described in the Japanese published patent 2-40767. Between the front roller pair of the drafting unit and a delivery roller pair arranged downstream thereof, the drafted fiber strand runs in this apparatus through a draft-free section, in which the fiber strand is in contact with a suction roller rotating transversely to the transport direction of the fiber strand. The suction roller imparts a certain false twist to the fiber strand and thus condenses the fiber strand. As in the condensing zone the fiber strand is already drafted to the desired fineness, but is not yet strengthened by means of a twist, a movement of the sliding surface transversely to the transport direction of the fiber strand leads very quickly to an end break.
It is an object of the present invention to improve the above mentioned apparatus in that instead of a transversely extending suction roller, a sliding surface is provided which does not lead to end breaks.
This object has been achieved in accordance with the present invention in that the sliding surface is the front surface of a rotating disk, whose rotational axle extends essentially perpendicular to the transport direction of the fiber strand.
By means of embodiments according to the present invention, the sliding surface itself imparts to the fiber strand in the condensing zone a motion component in transport direction, without deviating the fiber strand too far from its original direction of motion. The transport direction is determined practically by means of the form of the suction slit, while the sliding surface itself contributes mechanically thereto that the fiber strand can follow the direction of the suction slit also. The drafted, still untwisted fiber strand is hereby pneumatically condensed in that edge fibers are rolled in around the core strand. By means of this condensing, the fiber strand receives a better substance utilization, which leads to a greater evenness and a higher tensile strength of the yarn to be spun and simultaneously to a reduced hairiness.
The diameter of the disc should correspond approximately to the distance of the nipping lines between the front roller pair and the delivery roller pair. The disc should extend deep into the wedge-shaped gaps of the above mentioned two roller pairs and hereby have almost contact to the roller pairs. This is then achieved when the disc has approximately a diameter of 25 mm in the case of the spinning of cotton. This embodiment of the present invention results in the advantage that the rolled-in fiber ends do not roll back out again.
The suction slit should also extend as far as possible into the nipping line of the delivery roller pair. This supports the above mentioned measures effectively.
The width of the suction slit is wider than the width of the drafted fiber strand. This applies in particular there where the fiber strand is already condensed. When the fiber strand runs into the condensing zone, it is possible that it is wider than the suction slit; it is, however, important that as a result of the larger width of the suction slit, air can flow past both sides of the fiber strand. Only then is a pneumatic condensing possible by means of pneumatic transverse forces. The pneumatic condensing is supported by the false twist which the disk, by means of its rotation, imparts to the fiber strand.
At least in the area of the axle of rotation of the disk it is provided that the suction slit extends approximately parallel to the periphery of the disc. This results in a boomerang-shaped suction slit, which at first moves somewhat laterally transversely away from the entrance to the condensing zone and then is guided back after a small deflection. This embodiment according to the present invention permits the current transport direction of the fiber strand to follow approximately the peripheral direction of motion of the disc. The fiber strand to be condensed obtains thus almost in the entire condensing zone a component of motion in the transport direction despite its lateral deflection. End breaks in the condensing area can thus be effectively avoided.
The disk is provided /with a plurality of holes, whose diameter measures between 0.5 mm and 0.8 mm, according to the thickness of the disc. These relatively large diameters of the holes result in the advantage that the holes are not covered by fiber fly during suction.
It is favorable when the peripheral speed of the disk in the area of the suction slit is significantly greater than the transporting speed of the fiber strand. Speeds of approximately 400 to 500 rpm are preferred. Hereby, the rotating disc, so to speak, slides away from under the fiber strand, whereby the rolling-in of the edge fibers is additionally supported.
The condensing effect is improved when the sliding surface, according to the material of the fibers to be spun, is provided with a suitable plating, for example with a nickel-diamond plating. Tests should establish which plating is most suited to the purpose. The plating does not primarily serve wear protection, but rather serves first and foremost the improvement of the spinning quality.
In an advantageous embodiment of the present invention, the disc is applied to the rotational axle in such a way that it can be easily removed, for example by means of a magnet holding device. The disc can be easily removed for cleaning without disassembly of further parts, or the disc can be exchanged for one suitable to the fiber material to be spun, for example when another plating or another hole size has to be applied.